Transparent film-forming compositions for magnetic recording

Abstract

A concentrated fine solid particle dispersion useful for forming a substantially photographically transparent magnetic recording layer is disclosed, comprising an organic solvent medium containing a dispersing agent and dispersed magnetic particles, wherein the magnetic particles are present at a concentration of at least 25% by weight and the organic solvent medium is comprised primarily of organic solvent selected from dimethyl succinate, dimethyl glutarate and dimethyl adipate. This invention provides a stable concentrated dispersion of magnetic particles useful for preparing substantially photographically transparent magnetic recording layers. A film-forming binder solution can be added to dilute the concentrated dispersion, which then can be applied to a support to form a transparent magnetic layer for a magnetic recording element. This invention also provides a photographic element which contains a magnetic recording layer which has excellent magnetic characteristics and which is substantially photographically transparent by virtue of its low granularity and optical density.

1. A concentrated fine solid particle dispersion useful for forming a substantially photographically transparent magnetic recording layer, comprising an organic solvent medium containing a dispersing agent and dispersed magnetic particles, wherein the magnetic particles are present at a concentration of at least 25% by weight and the organic solvent medium is comprised primarily of organic solvent selected from dimethyl glutarate and dimethyl adipate. 
     
     
       2. A dispersion according to  claim 1 , wherein the dispersing agent comprises a fatty acid amine, polyvinyl pyrrolidone, polyvinyl alcohol, quaternary amine, phosphoric acid ester, or polyester-polyamine. 
     
     
       3. A dispersion of  claim 2 , wherein the dispersing agent comprises a poly (C 2-4 -alkyleneimine) polymeric dispersant carrying at least two mono- or poly-(carbonyl-C 1-7 -alkyleneoxy) groups. 
     
     
       4. A dispersion according to  claim 1 , wherein the organic solvent medium is comprised primarily of dimethyl glutarate. 
     
     
       5. A dispersion according to  claim 1 , wherein the magnetic particle comprise Co surface treated γ-Fe 2 O 3  having a specific surface area of greater than 40 m 2 /g. 
     
     
       6. A dispersion according to  claim 1 , wherein the magnetic particles are present at a concentration of at least 49 weight percent. 
     
     
       7. A process for the preparation of a concentrated fine solid particle dispersion of magnetic particles in accordance with  claim 1  useful for forming a magnetic recording layer, which comprises:
 (a) forming a slurry of at least 25 weight percent solid magnetic particles and a dispersing agent in an organic solvent medium comprised primarily of organic solvent selected from dimethyl glutarate and dimethyl adipate; and  
 (b) milling the slurry for a period of time sufficient to ensure that substantially no agglomerates of the magnetic particles are present.  
 
     
     
       8. A process according to  claim 7 , further comprising
 (c) mixing a solution of a film-forming polymeric binder with the milled concentrated magnetic particle dispersion to form a diluted composition comprising less than 25 weight percent magnetic particles.  
 
     
     
       9. A process according to  claim 8 , wherein the polymeric binder comprises a cellulose ester or mixture of cellulose esters. 
     
     
       10. A process according to  claim 8 , wherein the diluted composition comprising less than 10 weight percent magnetic particles. 
     
     
       11. A process according to  claim 8 , wherein the diluted composition comprising less than 5 weight percent magnetic particles. 
     
     
       12. A process for making a magnetic recording element comprising a support and a transparent magnetic recording layer coated thereon, wherein the process comprises combining a film-forming binder and a dispersion of magnetic particles in accordance with  claim 1  to form a coating composition and applying said coating composition onto the support to form the transparent magnetic recording layer. 
     
     
       13. A process for making a photographic element comprising a photographic support, a light sensitive layer and a substantially photographically transparent magnetic recording layer, wherein the process comprises combining a film-forming binder and a dispersion of magnetic particles in accordance with  claim 1  to form a coating composition and applying said coating composition onto said photographic support to form the substantially photographically transparent magnetic recording layer. 
     
     
       14. A process for making a photographic element according to  claim 13 , wherein the polymeric binder comprises a cellulose ester or mixture of cellulose esters.